The food wasn't all that good, but the party was a success in every other way.
Literal
Cooking [topic-は] that-much delicious [contrastive-は] was-not [though-けれど], other [possessive-の] points [in-では] party [topic-は] succeeded.
そう ('that much') paired with a negative softens the criticism. けれど functions as a softer, more conversational concessive than が. The contrastive は after おいしく reinforces the contrast — 'as for being delicious, it wasn't' — a layer of emphasis beyond simply おいしくなかった.